One of the most recurrent forms of Mahakala is the one-head and two-hand form known as panjarnata/panjara nata (gurgyi gompo in Tibetan) – for the full and more accurate name and meaning see the Himalayan Art Resources website. Easy to recognise, he squats on a victim and holds a flaying knife and a skull cup before his heart and has a danda stick (missing here) balancing over both arms.
18th century, Tibet, Mahakala, mGon dkar (labelled son-dkar), bronze, at the Metropolitan Museum of Art in New York (USA). Called cintimani sita in sanskrit, this form has one head and six arms, the main right hand holding a wish-granting jewel at heart level. The other right hands hold a flaying knife and a drum, the left ones hold a (broken) trident, an elephant goad and a skull cup with a long-life vase in it.
The four-hand form (chaturbhuja) of this wrathful deity may hold a variety of attributes. The above holds a skull cup in his left hand and a heart-shaped lotus bud on the other side. The upper hands hold a flaming sword and a staff. He wears the usual wrathful ornaments including a five-skull cup, a garland of severed heads and a long snake worn as a sacred cord.
Generally speaking, male deities with a wrathful appearance wear a tiger skin loin cloth, marked with flame-like stripes, and females wear a leopard skin, marked with star-like dots. The above appears to be wearing a leopard skin.
On this much older example he is seated on a victim. He wears a tiger skin that completely covers his legs and his right foot rests on a large lotus fastened to the base, in the Indian fashion (Pala period).